(1) Field of the Invention
This invention relates to an improvement to a warning device suitable for use in a passive seat belt system in which an occupant-restraining webbing is automatically brought into contact with or out of contact from the body of an occupant. When a slider is in an occupant-restraining position, the warning device detects in a contactless fashion by a magnetic flux sensor whether or not a tongue fastened to one end of a webbing is latched in an emergency release buckle movable along with the slider. If they are found unlatched, the warning device urges the occupant to wear the webbing.
(2) Description of the Related Art
One example of passive seat belt systems to which a conventional warning device is applied is illustrated in FIG. 17. A residual portion of an occupant-restraining webbing 1 is taken up in an inner retractor 3 provided on a lower part of an inboard wall of a seat 2, while a free end portion of the webbing 1 is connected to a slider 5 by way of an emergency release buckle 4. The slider 5 is received movably back and forth along the length of a vehicle in a slide rail 7 mounted on a roof side of an inner wall of a roof of the vehicle. The slider 5 is driven by an unillustrated drive member such as a drive wire or drive tape which is paid out or taken up by a drive unit 8 operable responsive to each opening or closure of an associated door, so that the slider 5 is caused to move in and along the slide rail 7. Inside the drive unit 8, there is provided a reel (not shown) connected to an unillustrated motor. The drive member is wound on the reel, so that the drive member can be paid out or taken up. An anchor latch 9 is provided on a rear end portion of the slide rail 7. Extending between the anchor latch 9 and the drive unit is a guide tube 10 made of a synthetic resin and adapted to guide movement of the drive member.
FIG. 17 also shows tube brackets 11 fixing the guide tube 10 on a body 6 of the vehicle, a limit switch 12 for detecting each displacement of the slider 5 to the frontmost end of the slide rail 7, and rail brackets 13 fixing the slide rail 7 on the body 6 of the vehicle.
To urge the fastening of the webbing 1 and to prevent any false detection of latching between the tongue 14 fastened to an end portion of the webbing 1 and the emergency release buckle in spite of actual unlatching thereof, such a passive seat belt system is provided with a warning device which is constructed of a magnet provided on the slider 5 and a magnetic flux sensor provided on the side of the body of the vehicle. The magnetic flux sensor is ON-OFF controlled by the existence or absence of a magnetic flux or field.
According to the above construction, except when the tongue 14 is latched in the emergency release buckle 4 and the slider 5 is firmly restrained in the anchor latch 9, the magnetic flux sensor is turned off so that a warning means connected to the magnetic flux sensor is actuated to achieve the designed object.
However, the magnetic flux sensor is actuated responsive to a magnetic flux or force in the conventional warning device for the passive seat belt system. If a device having a magnet, for example, a speaker, an electric motor or the like is brought close the magnetic flux sensor, the magnetic flux sensor is actuated in a false by the magnetic force of the magnet, leading to a potential problem that the reliability of the warning device for the passive seat belt system may be impaired.